Fertilization in plants is the fusion of male and female gametes to form a zygote, the initial step in sexual reproduction, occurring after pollination and germination. It's a complex physicochemical process.
Here's a breakdown:
1. Pollination:
- Pollen grains, containing the male gametes, are transferred from the stamen (male part) to the pistil (female part) of a flower. This can happen through wind, water, insects, or other animals.
2. Germination of Pollen Grain:
- Once a pollen grain lands on the stigma (the receptive surface of the pistil), it germinates, forming a pollen tube. This pollen tube grows down through the style (the stalk of the pistil) toward the ovary.
3. Growth of the Pollen Tube:
- The pollen tube acts as a pathway for the male gametes (sperm cells) to reach the ovule(s) within the ovary.
4. Entry into the Ovule:
- The pollen tube enters the ovule, often through a small opening called the micropyle.
5. Double Fertilization (Unique to Angiosperms - Flowering Plants):
- Here's where it gets interesting. Angiosperms undergo a process called double fertilization:
- One sperm cell fuses with the egg cell (ovum) to form a diploid zygote (2n). This zygote develops into the embryo of the seed.
- The other sperm cell fuses with the polar nuclei (usually two) in the central cell of the ovule to form a triploid (3n) endosperm. The endosperm serves as a nutrient-rich tissue to nourish the developing embryo.
6. Development:
- After fertilization, the ovule develops into a seed, and the ovary develops into a fruit, which aids in seed dispersal.
In summary, fertilization in plants involves pollination, pollen tube growth, and the fusion of male gametes with the egg cell and polar nuclei within the ovule, leading to the formation of a zygote and endosperm. The endosperm provides essential nutrients to the developing embryo.
